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# GMATprep DS: Number theory II

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VP
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GMATprep DS: Number theory II [#permalink]

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09 Feb 2007, 03:25
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Director
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09 Feb 2007, 08:57

In any case there can 7 numbers that meet the criterion.
Manager
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09 Feb 2007, 10:29
Tricky statement is 2<= n <=15

For stmnt 1.
========
a(1) = 24
If K is +ve then all are more than 10. If K is -24 all can be -ve so CANNOT decide.

For stmnt 2.
========
If a(8) = 10 then if K is +ve then all the elements for n > 8 are > 10.

If K -ve all the elements for n < 8 are > 10.

I would have chosen B actually I did. Then I reliased that n can only go up to 2.

In that case I would go with C.

OA please on this. I need to check whether this has a trap or not.

vineet
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Re: GMATprep DS: Number theory II [#permalink]

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09 Feb 2007, 11:00
kripalkavi wrote:

Coniditon1: a1 = 24

a2 = a1 + k = 24 + k
a3 = a2 + k = 24 + 2k

a15 = 24 + 14k

we can keep on doing this but we will not be able to find all the values as we don't know the value of k it can be negative or positive. So it is hard to say how many values are greater
than 10.

a8 = a7 + k = 10 ==> a7 = 10-k
a9 = a8 + k = 10 + k

a7 = 10-k
a8 = 10
a9 = 10+k

if k is psotive we know all the value greater than a8 will be greater than 10
if k is negative we know all the values less than a8 will be greater than 10

and that number will be 7 terms so condition 2 is sufficient answer is B
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VP
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Location: Bangalore
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Re: GMATprep DS: Number theory II [#permalink]

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10 Feb 2007, 04:36
amorpheus wrote:
kripalkavi wrote:

Coniditon1: a1 = 24

a2 = a1 + k = 24 + k
a3 = a2 + k = 24 + 2k

a15 = 24 + 14k

we can keep on doing this but we will not be able to find all the values as we don't know the value of k it can be negative or positive. So it is hard to say how many values are greater
than 10.

a8 = a7 + k = 10 ==> a7 = 10-k
a9 = a8 + k = 10 + k

a7 = 10-k
a8 = 10
a9 = 10+k

if k is psotive we know all the value greater than a8 will be greater than 10
if k is negative we know all the values less than a8 will be greater than 10

and that number will be 7 terms so condition 2 is sufficient answer is B

Awesome explanation! OA is B.
Re: GMATprep DS: Number theory II   [#permalink] 10 Feb 2007, 04:36
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